Proper coordination of neural crest migration is an absolute requirement for normal cardiovascular development - most particularly outflow tract morphogenesis. The gap junction protein Cx43 has a key function in this directed migration of cardiac neural crest cells. The molecular mechanism by which Cx43 affects neural crest motility is unknown. The forces driving cell migration are generated largely by the dynamics of the actin cytoskeleton. We hypothesize that proteins mediating linkage between connexins and actin are candidates for regulators of cell motility. One molecule known to mediate interaction between connexins and actin is ZO1 - a PDZ protein related to the Drosophila tumor suppressor protein discs large. The Gourdie lab has shown that Cx43-ZO1 interaction is critical to developmental remodeling of the extentof gap junctional contact between myocardial cells. Furthermore, we have data showing that inhibition of ZO1- Cx43 interaction decreases neural crest outgrowth in vitro and reduces motility of fibroblasts and epithelial cells in cultured monolayers in a "scratch wound" migration assay. We will test the hypothesis that ZO1-Cx43 interaction is an integral part of a mechanism involved in regulation of cell-cell contact pattern and migration of neural crest cells by determining: 1. Whether factors known to stimulate neural crest cell motility, affect interactions between Cx43, ZO-1 and other connexin interacting proteins in vitro; 2. Whether inhibition of ZO1-Cx43 interaction is sufficient to disrupt regulation of the rate and directionality of neural crest cell migration in vitro; and 3. if ZO1-Cx43 interaction is necessary for the directed migration of neural crest cells in vivo. This study will provide new insight into molecular regulation of neural crest migration in the embryo and origins of birth defects in humans. ;